The first image dates to Sept. 4 and shows the coin used to help calibrate Curiosity's camera and test its performance. The penny is coated with Mars dust, a reminder of the powerful storm that knocked NASA's Opportunity rover out of contact in June.
The second image is from Dec. 2 and shows a much cleaner penny. "Dust has certainly been blowing around in Gale Crater lately," writes Fraeman.
Curiosity's clean coin may help boost optimism about the Opportunity rover, which went into hibernation when dust covered its solar panels and cut off its power. NASA is still hopeful that winds will clean the panels and allow the rover to recharge and make contact.
Curiosity is currently investigating a group of red Jura rocks and the team hopes to find a suitable site for drilling to get a better understanding of their geology. It'll be doing so with a much less dusty rover than they had weeks ago.